Grooved adhesive tape

ABSTRACT

The aim of the invention is to improve an impairment to the adherence of an adhesive tape to a substrate caused by the inclusion of air bubbles between the adhesive tape and the substrate. According to the invention, said aim is achieved by means of an adhesive tape which comprises at least one adhesive layer, wherein the adhesive layer has at least one groove and none of the grooves extends as far as one of the lateral edges of the adhesive layer. The invention further relates to a release liner having a surface which has at least one ridge, wherein none of the ridges extends as far as one of the lateral edges of the release liner.

This application is a 371 of International Patent Application No.PCT/EP2013/066203 filed Aug. 1, 2013, which claims foreign prioritybenefit under 35 U.S.C. §119 of the German Patent Application No. 102012 215 345.4, filed Aug. 29, 2012, the disclosures of which patentapplications are incorporated herein by reference.

The invention is situated within the technical field of adhesive tapes.The invention relates in particular to adhesive tapes having aparticular topography in the surface of an adhesive layer.

Adhesive tapes are used in a wide variety of ways to join substrates,but also, for example, as masking tapes or insulating tapes. Animportant role in the context of bonds with adhesive tapes is played bythe nature of the contact area between adhesive and substrate. Thiscontact area may be adversely affected by a variety of externalinfluences, these influences leading in general to a reduction in theavailable contact area, in turn causing the quality of the target bondto drop. The contact area may be reduced, for example, by air inclusionsbetween adhesive and substrate. This is frequently manifested inimprecise bonds and/or in bonds which lack strength and durability.

The precise positioning of substrates to be bonded is vital, forexample, in flexographic printing processes. These are rotationalprinting processes where flexible printing plates made from photopolymeror rubber are utilized, the plates having a relief corresponding to theinformation to be applied by printing. These printing plates or printingforms are fastened on a printing cylinder. This is done using adhesivetapes which by virtue of their compressibility properties substantiallyinfluence the print quality.

In the printing process, the printing plate then passes through an inkreservoir, where the relief takes up the printing ink. The printingcylinder then transports the printing plate to a transfer station, wherethe surface containing printing ink comes into contact with thesubstrate to be printed. On removal of the printing plate from thesubstrate, the film of printing ink splits and leaves behind an imprintcorresponding to the relief present on the printing plate surface. Inktransfer requires precise monitoring of the applied pressure whenplacing the printing plate onto the substrate, this pressuresubstantially determining the thickness of application and theuniformity of the printed image.

A double-sided adhesive tape is typically used for fastening theprinting plate on the printing cylinder. In order to ensure high printquality, the printing plate must be very carefully mounted on theprinting cylinder and precisely positioned. It is oftentimes necessaryfor the position of the plate to have to be adjusted a number of times.In the course of the mounting of the plate on the printing cylinder, andin the course of possible repositioning, the inclusion of air occursfrequently at the interfaces between printing plate and adhesive tapeand/or between adhesive tape and carrier or printing cylinder. Airbubbles of this kind lead to changes in the pressure applied whenplacing the printing plate onto the substrate, and constitute one of themost frequent sources of error in flexographic printing processes.

While it is possible in principle to remove the air inclusions usingsyringes or knives, these tools may also cause damage to the printingplates. Attempts have therefore been made to counter the inclusion ofair bubbles by specific adhesive tape architectures. For instance,adhesive tapes with adhesive in a parallel stripe or corrugated patternhave been used. Such adhesive tapes, however, have proven to lacksufficient reliability in terms of the bonding quality achieved.Although they did allow air to escape efficiently from the interfaces,the bonding effect between carrier and printing plate lack sufficientreliability, especially at high throughput rates. Adhesive tapes with anirregular relief of adhesive were also trialed, but likewise gaveinadequate bonding strengths and, moreover, continued to have airinclusions in certain regions.

U.S. Pat. No. 5,296,277 describes an adhesive tape having a number ofelevations in the adhesive layer, these elevations having flattened,adhesive tips whose area is less than 25% of the total area of theadhesive layer.

U.S. Pat. No. 5,362,516 describes the structuring of the surface of anadhesive layer by means of beads which are applied beforehand and overwhich the adhesive is then spread. A similar construction is subjectmatter of U.S. Pat. No. 5,141,790, in which case the structuring isachieved via particles which are incorporated into the adhesive layerand whose tips are substantially free of adhesive.

GB 1 511 060 describes an adhesive layer having at least one relativelylong ridge or cutout, with at least one of these structures breakingthrough the outer edge of the adhesive layer.

U.S. Pat. No. 5,268,228 describes a double-sided adhesive tape havingjoints in the adhesive layer on one or both sides, the purpose of thesejoints being to divert the air during bonding, and their size being suchthat they very largely disappear after bonding.

WO 98/29516 A1 as well relates to adhesive layers with an embossedrelief, and describes a method for controlling the topography of anadhesive surface, wherein the relief or topography of the adhesive layercontrols the bonding performance.

WO 02/11985 A1 describes adhesive tapes for use in flexographic printingprocesses, the tapes having a regular pattern of permanent channels.Furthermore, the specification describes flexographic printing processesand other components of an apparatus for flexographic printing.

The measures known to date for preventing air inclusions provide for theair to be carried away outwardly. As a result, however, the problem ofcapillary effects—which may even cause air to be drawn in—arisesfrequently. There are often disadvantages in the distribution of thewetting area and/or of the bond strengths, owing to the air removalchannels that are present in the adhesive layer, and this can lead todeficient bonds. It is possible, for example, that air is not taken offtoward the outside at all, but instead is merely shifted within theadhesive layer into the next cavity. Here there may be substantialaccumulations of air, which lower the accuracy of the bond and/or of thepositioning of the substrate. Furthermore, the contact area actuallyachieved between adhesive and substrate is heavily dependent on thepressure exerted.

It is an object of the invention, therefore, to provide an adhesive tapewith which the above problems can be overcome. The adhesive tape isintended in particular to counteract the displacement of air bubbleswithin the adhesive tape as a result of the prevailing applied pressure,and to allow largely constant bond areas and bond strengthsindependently of the applied pressure.

The achievement of this object is based on the idea that the includedair should not be diverted to the outside, but should instead bediverted into and held in defined recesses within the adhesive layer. Afirst subject of the invention, therefore, is an adhesive tape whichcomprises at least one adhesive layer, wherein the adhesive layer has atleast one groove and no groove extends to one of the side edges of theadhesive layer. An adhesive tape of this kind has no capillary effects,since it does not contain any continuous channels. Fluids, and inparticular air, are not draw into the bond area, therefore. The clearlydelimited and defined bonding area allow the imposition of relativelyconstant bond strengths, independently of the applied pressure, and theformation of new air bubbles under the influence of an applied pressureprevailing at certain locations of the adhesive tape is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe drawings, wherein:

FIG. 1 is a schematic illustrating a number of variants of grooves inthe adhesive layer.

FIG. 2 is a schematic of the adhesive layer, illustrating the meaning ofthe terms “groove depth” and “groove width”.

FIG. 3 is a plan view of a grooved adhesive layer and shows repeatingshapes that are present separately from one another.

FIG. 4 is a plan view of a grooved adhesive layer and shows repeatinggroove shapes that are partly separate from one another and partlyjoined to one another.

FIG. 5 is a plan view of a grooved adhesive layer and shows differentgroove shapes present separately from one another.

An “adhesive layer” means a layer of the adhesive tape of the inventionthat is able to enter into direct contact with a substrate and to adherethereto. With preference in accordance with the invention, the adhesivelayer is formed of a pressure-sensitive adhesive. This is a viscoelasticadhesive whose set film at room temperature in the dry state remainspermanently tacky and adhesive. Bonding takes place by gentle appliedpressure, immediately, to virtually all substrates.

The at least one adhesive layer of the adhesive tape of the inventionpreferably comprises a polymer selected from the group consisting ofnatural rubbers, synthetic rubbers, polyacrylates, silicones, andmixtures of two or more of the above polymers. More preferably the atleast one adhesive layer of the adhesive tape of the invention comprisesto an extent of at least 30 wt %, more preferably at least 40 wt %, andmore particularly at least 50 wt %, based on the total weight of theadhesive layer, a polymer selected from the group consisting of naturalrubbers, synthetic rubbers, polyacrylates, silicones, and mixtures oftwo or more of the above polymers.

Synthetic rubbers preferably comprise styrene-butadiene copolymers,block copolymers such as, for example, styrene-isoprene-styrene,styrene-butadiene-styrene, styrene-ethylene/butylene-styrene,styrene-ethylene/propylene styrene, and combinations of the abovecopolymers. Synthetic rubbers and natural rubbers are commonly usedtogether with at least one bond strength reinforcing resin. Examples ofbond strength reinforcing resins contemplated include polymers ofunsaturated C₅-C₉ hydrocarbons, terpene resins, and rosin.

By “polyacrylates” are meant polymers whose monomer base on anamount-of-substance basis is made up to an extent of at least 30% ofacrylic acid, methacrylic acid, acrylic esters and/or methacrylicesters, with acrylic esters and/or methacrylic esters being presentgenerally at least proportionally and preferably to an extent of atleast 30%. More particularly a “polyacrylate” is a polymer obtainable byradical polymerization of acrylic and/or methylacrylic monomers andalso, optionally, further, copolymerizable monomers.

Preference is given to using a polyacrylate which can be traced back tothe following monomer composition:

-   -   a) acrylic esters and/or methacrylic esters of the following        formula

CH₂═C(R^(I))(COOR^(II))

-   -    where R^(I) is H or CH₃ and R^(II) is an alkyl radical having 4        to 14 C atoms,    -   b) olefinically unsaturated monomers having functional groups        which are reactive toward epoxide groups, for example,    -   c) optionally further acrylates and/or methacrylates and/or        olefinically unsaturated monomers which are copolymerizable with        component (a).

For the application of the polyacrylate as a pressure-sensitiveadhesive, the proportions of the corresponding components (a), (b), and(c) are selected such that the product of polymerization has inparticular a glass transition temperature ≦15° C. (DMA at lowfrequencies).

For the preparation of pressure-sensitive adhesives, it is veryadvantageous to select the monomers of component (a) with a fraction of45 to 99 wt %, the monomers of component (b) with a fraction of 1 to 15wt %, and the monomers of component (c) with a fraction of 0 to 40 wt %(the figures are based on the monomer mixture for the “base polymer”, inother words without additions of possible additives to the completedpolymer, such as resins etc.).

In particular, the monomers of component (a) are plasticizing and/ornonpolar monomers. Preferred for use as monomers (a) are acrylic andmethacrylic esters with alkyl groups consisting of 4 to 14 C atoms, morepreferably 4 to 9 C atoms. Examples of such monomers are n-butylacrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentylmethacrylate, n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate,n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonylacrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate,and their branched isomers, such as 2-ethylhexyl acrylate or2-ethylhexyl methacrylate, for example.

In particular, the monomers of component (b) are olefinicallyunsaturated monomers having functional groups, in particular havingfunctional groups which are able to enter into a reaction with epoxidegroups.

For component (b), preference is given to using monomers with functionalgroups which are selected from the group encompassing the following:hydroxyl, carboxyl, sulfonic acid or phosphonic acid groups, acidanhydrides, epoxides, amines.

Particularly preferred examples of monomers of component (b) are acrylicacid, methacrylic acid, itaconic acid, maleic acid, fumaric acid,crotonic acid, aconitic acid, dimethylacrylic acid,β-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid,vinylphosphonic acid, itaconic acid, maleic anhydride, hydroxyethylacrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate,hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol,glycidyl acrylate, glycidyl methacrylate.

In principle it is possible as component (c) to use all vinylicallyfunctionalized compounds which are copolymerizable with component (a)and/or with component (b). The monomers of component (c) may serve toadjust the properties of the resultant pressure-sensitive adhesive.

Exemplary monomers of component (c) are as follows:

methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate,ethyl methacrylate, benzyl acrylate, benzyl methacrylate, sec-butylacrylate, tert-butylacrylate, phenyl acrylate, phenyl methacrylate,isobornyl acrylate, isobornyl methacrylate, tert-butyl phenyl acrylate,tert-butylphenyl methacrylate, dodecyl methacrylate, isodecyl acrylate,lauryl acrylate, n-undecyl acrylate, stearyl acrylate, tridecylacrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentylmethacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate,2-butoxyethyl methacrylate, 2-butoxyethyl acrylate,3,3,5-trimethylcyclohexyl acrylate, 3,5-dimethyladamantyl acrylate,4-cumylphenyl methacrylate, cyanoethyl acrylate, cyanoethylmethacrylate, 4-biphenylyl acrylate, 4-biphenylyl methacrylate,2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofurfurylacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate,dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,2-butoxyethyl acrylate, 2-butoxyethyl methacrylate, methyl 3-methoxyacrylate, 3-methoxybutyl acrylate, phenoxyethyl acrylate, phenoxyethylmethacrylate, 2-phenoxyethyl methacrylate, butyldiglycol methacrylate,ethylene glycol acrylate, ethylene glycol monomethyl acrylate, methoxypolyethylene glycol methacrylate 350, methoxy polyethylene glycolmethacrylate 500, propylene glycol monomethacrylate, butoxydiethyleneglycol methacrylate, ethoxytriethylene glycol methacrylate,octafluoropentyl acrylate, octafluoropentyl methacrylate,2,2,2-trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropylacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate,2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,4,4,4-heptafluorobutylmethacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate,2,2,3,3,4,4,4-heptafluorobutyl methacrylate,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-penta-decafluorooctyl methacrylate,dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide,N-(1-methylundecyl)acrylamide, N-(n-butoxymethyl)acrylamide,N-(butoxymethyl)methacrylamide, N-(ethoxymethyl)acrylamide,N-(n-octadecyl)acrylamide, and also N, N-dialkyl-substituted amides,such as, for example, N,N-dimethylacrylamide,N,N-dimethylmethacrylamide, N-benzylacrylamides, N-isopropylacrylamide,N-tert-butylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide,N-methylolmethacrylamide, acrylonitrile, methacrylonitrile, vinylethers, such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutylether, vinyl esters, such as vinyl acetate, vinyl chloride, vinylhalides, vinylidene chloride, vinylidene halides, vinylpyridine,4-vinylpyridine, N-vinylphthalimide, N-vinyllactam, N-vinylpyrrolidone,styrene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene,4-n-decylstyrene, 3,4-dimethoxystyrene. Macromonomers such as2-polystyreneethyl methacrylate (molecular weight Mw of 4000 to 13 000g/mol), poly(methyl methacrylate)ethyl methacrylate (Mw of 2000 to 8000g/mol).

Monomers of component (c) may advantageously also be selected such thatthey contain functional groups which support subsequent radiationcrosslinking (for example by electron beams, UV). Suitablecopolymerizable photoinitiators are, for example, benzoin acrylate andacrylate-functionalized benzophenone derivatives. Monomers which supportcrosslinking by electron beam bombardment are, for example,tetrahydrofurfuryl acrylate, N-tert-butyl acrylamide, and allylacrylate.

The polyacrylates may be prepared by methods familiar to the skilledperson, especially advantageously by conventional radicalpolymerizations or controlled radical polymerizations. The polyacrylatesmay be prepared by copolymerizing the monomeric components, using thecustomary polymerization initiators and also, optionally, chain transferagents, with polymerization taking place at the customary temperaturesin bulk, in emulsion, in water or liquid hydrocarbons for example, or insolution.

The weight-average molecular weights M_(w) of the polyacrylates arepreferably in a range from 20 000 to 2 000 000 g/mol, very preferably ina range from 100 000 to 1 000 000 g/mol, extremely preferably in a rangefrom 150 000 to 500 000 g/mol [the figures for the average molecularweight M_(w) and for the polydispersity PD in this specification relateto the determination by gel permeation chromatography]. To this end itmay be advantageous to conduct the polymerization in the presence ofsuitable chain transfer agents such as thiols, halogen compounds and/oralcohols, in order to set the desired average molecular weight.

Silicones are preferably polydiorganosiloxanes having a number-averagemolecular weight of about 5000 to about 10 000 000, more particularly ofabout 50 000 to about 1 000 000, and/or copolymeric silicone resins,also designated as MQ resins, with a number-average molecular weight ofabout 100 to about 1 000 000, more particularly of about 500 to about 50000. the MQ resins contain triorganosilyloxy units and also SiO_(4/2)units. Silicone-based pressure-sensitive adhesives customarily comprise20 to 60 parts by weight of polydiorganosiloxanes and 40 to 80 parts byweight of one or more MQ resins. The aim is usually for a reaction ofthe polydiorganosiloxanes with the MQ resins, in order for adhesiveproperties to be developed. A reaction of this kind may be, for example,a condensation reaction between silanol functionalities present in theMQ resin and terminal silanol groups of the diorganopolysiloxanes. Afurther possible reaction pathway is formed by addition reactionsbetween alkenyl functionalities of the polydiorganosiloxanes and SiH,alkenyl and/or silanol functionalities of the MQ resins.

The at least one adhesive layer of the adhesive tape of the inventionmay comprise additives which may contribute to the emphasizing ofparticular properties of the adhesive layer. These additives may be, forexample, pigments, plasticizers, fillers, stabilizers, antioxidants,etc. The proportion of the additives in the adhesive layer is preferablyfrom 0.1 to 50 wt %, based on the total weight of the adhesive layer.

The weight per unit area of the adhesive layer is preferably not morethan 200 g/m², more preferably not more than 100 g/m², and moreparticularly 40 to 100 g/m², as for example 60 to 100 g/m². The statedweight per unit area relates to the fully embossed regions of theadhesive layer, and hence not to the grooves provided in accordance withthe invention.

Likewise preferably, the adhesive layer is a coherent adhesive layer.This means an adhesive layer which parallel to its surface has a planewith an adhesive layer which is present continuously, i.e., is unbrokenat any location. A coherent adhesive layer will of course have thegroove or grooves provided in accordance with the invention, but in thecase of a coherent adhesive layer, these grooves must not be so deepthat the adhesive layer is interrupted. Provided that the surface of theadhesive layer lies substantially in the x-y plane, accordingly, in thecase of a coherent adhesive layer, a section parallel to the x-y planein a defined depth z must result in adhesive being present at everypoint in the sectional plane. The surface of the adhesive layer isregarded as being the boundary with the surrounding medium on the sideof the adhesive layer that faces the substrate to be bonded; forcalculations and for definitions relating to the surface area, thesurface area occupied by the grooves is equated with the groove “basearea” situated in the plane of the adhesive layer. Accordingly, in thecase of a groove, the surface area will be regarded as continuing in thesame plane as the adhesive-comprising surface.

The adhesive tape in accordance with the invention may be either asingle-sided or a double-sided adhesive tape.

A “groove” means a macroscopically perceptible recess within theadhesive layer, beginning in the surface of the adhesive layer, and ablein principle to have any desired shape and depth. Using therepresentation of a cut made through an adhesive tape of the invention,in the direction of the layer sequence at an angle of 90° to the runningdirection of the grooves, FIG. 1 illustrates a number of variants ofgrooves in the adhesive layer. The reference numerals in the figure havethe following meanings:

-   1—carrier-   2—adhesive layer-   3—grooves.

With preference in accordance with the invention, the groove depth is atleast 10 μm, more preferably at least 20 μm, more particularly at least25 μm, as for example at least 30 μm. The “groove depth” means themaximum extent of a groove perpendicular to the plane in which thesurface of the adhesive layer is situated. The surface of the adhesivelayer is situated on the substrate-facing side of the adhesive layer.Likewise preferably, the groove depth is not more than 200 μm, morepreferably not more than 100 μm, more particularly not more than 60 μm,as for example not more than 50 μm.

Furthermore the depth of all grooves varies preferably by not more than20%. The uniform topography that is achieved in this way ensuresconsistent bonding properties over the full extent of the adhesive tape.

With preference in accordance with the invention, the groove width is 10to 200 μm. The “groove width” means the maximum distance of the grooveedges from one another at an angle of 90° to the running direction ofthe groove, at any desired location in the groove.

Using the representation of a cut made through an adhesive tape of theinvention parallel to the layer sequence and at an angle of 90° to therunning direction of the grooves, FIG. 2 illustrates the meaning of theterms “groove depth” and “groove width”. The meaning of the referencenumerals in the figure is as follows:

-   1—carrier-   2—adhesive layer-   3—grooves-   a, a′—groove width-   b, b′—groove depth.

In accordance with the invention, no groove extends to one of the sideedges of the adhesive layer. This means that no groove has contact withan edge which delimits the surface of the adhesive layer or any face ofthe adhesive layer that lies below the surface and parallel to the planeof the surface. Instead, there is always at least a minimum amount ofadhesive between groove and edge. The design of the groove structure ofthe adhesive tape of the invention therefore differs from conventionaltopographies, which provide continuous channels, in contact with sideedges, for transporting air away. With the adhesive tape of theinvention, the disadvantages of such designs that have already beenlisted can be avoided, without air inclusions affecting the quality ofbonding. The distance between side edge of the adhesive tape and thegrooves is preferably at least 1 mm.

The air volume enclosed by the adhesive tape of the invention, and theachievable substrate wetting area, are preferably in a ratio to oneanother such that pressure stresses and shear stresses that occur in theassembly operation and during the use of the adhesive tape are unable todisplace the air. The nongrooved surface of the adhesive layer ispreferably 50% to 99%, more particularly 70% to 95%, and very preferably75% to 90% of the total surface area of the adhesive layer.

The at least one groove is preferably a permanent groove. This meansthat the rheological properties of the adhesive layer are set in such away that the adhesive layer topography determined by the groove orgrooves is durably retained in its essential extent during the intendedutilization of the adhesive tape of the invention. More preferably,“permanent groove” means that the topography is retained in itssubstantial extent even after multiple utilization of the adhesive tapeor after utilization over a relatively long time, as for example overseveral hours at 20 to 80° C. This permanence of the groove or groovesensures that even if the adhesive tape comes under multiple orrelatively long-lasting stress, air can be accommodated in the recessesintended for that purpose, and hence exact adhesive bonds are possible.

The geometric form of the profile of the grooves is in principle freelyselectable and may comprise, for example, lines, circles, polygonsand/or amorphous structures. Also possible are indicia, logos, or thelike. Repeating patterns may join one another or be present separatelyfrom one another. FIGS. 3 to 5 show in each case a plan view of thegrooved adhesive layer of an adhesive tape of the invention, andillustrate possible groove shapes. FIG. 3 shows repeating shapes thatare present separately from one another. FIG. 4 shows repeating grooveshapes that are partly separate from one another and partly joined toone another. FIG. 5 shows different groove shapes present separatelyfrom one another. The meanings of the reference numerals in each caseare as follows:

-   2—adhesive layer-   3—grooves.

The grooves may, furthermore, in a section in the direction of the layersequence and at an angle of 90° to their running direction, likewisehave in principle any desired form, comprising—for example—triangular,rectangular, or semicircular variants. Some of these forms are alreadyevident from FIG. 1.

The adhesive tape of the invention may comprise further layers. Theadhesive tape of the invention preferably comprises a furtherpressure-sensitive adhesive on the outside of the adhesive tape,opposite the grooved adhesive layer, and/or a stabilizing film, whichmay be a PET film, for example, and/or a foam layer and/or a laminatingadhesive.

The further pressure-sensitive adhesive may be a pressure-sensitiveadhesive having grooves in accordance with the invention. Thestabilizing film advantageously increases the resistance of the adhesivetape of the invention to tension, and thereby simplifies its demounting.The foam layer increases the printing quality. The laminating adhesiveserves in particular for the fixing of the stabilizing film on the foam.

The adhesive tape of the invention includes, for example, the followinglayers in the stated sequence:

-   -   grooved pressure-sensitive adhesive    -   stabilizing film    -   laminating adhesive    -   foam layer    -   further pressure-sensitive adhesive (grooved or nongrooved).

Also possible is an above construction where there is no laminatingadhesive, where the stabilizing film is nevertheless surrounded on bothsides by a layer of polyethylene, which has been applied in the form ofa liquid composition, for example, to the stabilizing film.

A further subject of the invention is a release liner having at leastone surface that features at least one ridge, wherein no ridge extendsto one of the edges of the release liner. With a release liner of thiskind, the structure defined by the ridges can be easily embossed intothe adhesive layer, and so the groove pattern described above can beproduced there.

A release liner—also referred to below simply as a liner—is a liningmaterial which has a nonstick (abhesive) surface and which is applieddirectly to an adhesive for temporary protection of the adhesive, andwhich can generally be removed by simple peeling immediately prior toapplication of the adhesive. Among other things, a release liner ensuresthat the adhesive is not soiled prior to use. In addition, releaseliners may be adjusted, by the nature and composition of the releasematerials, in such a way that the adhesive tape can be unwound with thedesired force (easily or with difficulty). Moreover, in the case ofadhesive tapes coated with adhesive on both sides, the release linerensures that the correct side of the adhesive is exposed first onunwind.

A liner is not part of an adhesive tape, but instead is just an aid toits production, storage, or for further processing. Furthermore, unlikean adhesive tape carrier, a liner is not joined permanently to a layerof adhesive; instead, the assembly is only temporary and not lasting.

A “ridge” means a macroscopically perceptible elevation that begins inthe surface of the liner and that may in principle have any desiredshape and height within the context of the invention. For possible formsand patterns of arrangement of the ridges in the liner, the commentsmade above concerning the grooves and the groove pattern of the adhesivelayer apply correspondingly. The geometric form of the profile of theridges is therefore in principle likewise freely selectable and mayinclude, for example, lines, circles, polygons and/or amorphousstructures. Also possible are indicia, logos, or the like. Repeatingpatterns may be joined to one another or be present separately from oneanother. In cross section, for example, the ridges comprise triangular,rectangular, or semicircular variants.

A “surface” of the liner is considered to mean the respective boundaryof the two sides of the liner with the surrounding medium; forcalculations and for definitions relating to the surface area, the areaoccupied by the ridges is equated with the base area at the foot of theridges. With preference in accordance with the invention, the areaoccupied by ridges, as a proportion of the liner surface featuring atleast one ridge, is 1% to 50%, more preferably 5% to 30%, and moreparticularly from 10% to 25%. The “area occupied by ridges” is the basearea of the surface in question that is occupied by ridges; the surfacearea of the ridge itself remains immaterial in this context.

In accordance with the invention, no ridge extends to one of the sideedges of the release liner. This means, in a sense corresponding to thegroove pattern of the adhesive tape of the invention, that no ridge hascontact with an edge that delimits the surface of the liner.

The ridge height of the release liner of the invention is preferably 10to 200 μm, more preferably 20 to 100 μm, more particularly 25 to 60 μm,for example 30 to 50 μm. The “ridge height” means the maximum extent ofa ridge perpendicular to the plane in which the surface of the liner islocated.

The ridge width at the foot of the ridge is preferably 10 to 200 μm. The“ridge width” means the maximum distance between two points at the footof the ridge from one another at an angle of 90° to the runningdirection of the ridge at any desired location on the ridge.

Measurement of the extent of the ridges in the liner of the inventionand of the grooves of the adhesive tape of the invention, particularlythe measurement of the ridge heights and groove depths, is accomplishedby means of scanning electron microscopy (SEM).

The liner of the invention may comprise at least one ridge on one sideor else on both sides.

The liner of the invention preferably comprises at least one carrier andat least one release material.

The carrier material of the liner of the invention preferably comprisesa polymer selected from the group consisting of propylene, moreparticularly monoaxially and biaxially oriented polypropylene,polyethylene terephthalate, polyethylene, polyvinyl chloride, andmixtures of two or more of the above polymers. More preferably thecarrier material of the liner of the invention comprises at least 30 wt%, more preferably at least 50 wt %, more particularly at least 70 wt %,as for example at least 90 wt %, of a polymer selected from the groupconsisting of polypropylene, more particularly monoaxially and biaxiallyoriented polypropylene, polyethylene terephthalate, polyethylene,polyvinyl chloride, and mixtures of two or more of the above polymers.The carrier material of the liner more preferably comprisespolypropylene or a triple extrudate with the following sequence:polyethylene-polypropylene-polyethylene.

As release agents or release material it is possible in principle to useall systems known to the skilled person. The release agent is preferablyselected from the group of silicone, fluorinated silicone, siliconecopolymers, waxes, carbamates, or mixtures of two or more of the statedsubstances.

The release agent may comprise solvent-borne and/or solvent-freesystems, with solvent-borne systems being preferred. The release agent,furthermore, may be radiation-crosslinking (by UV or electron beam),condensation-crosslinking, or addition-crosslinking; preferably it iscondensation-crosslinking.

Release agents used are preferably crosslinkable silicone systems. Theseinclude mixtures of crosslinking catalysts and what are called thermallycurable condensation-crosslinking or addition-crosslinkingpolysiloxanes. For condensation-crosslinking silicone systems, tincompounds such as dibutyltin diacetate are frequently present ascrosslinking catalysts in the composition.

The liner of the invention may also comprise paper coated with one ofthe above release agents.

The thickness of the liner, disregarding the ridges, is preferably 20 to200 μm.

A further subject of the invention is a method for generating at leastone groove in a surface of adhesive, at least comprising

the contacting of the surface of a material, said surface featuring atleast one ridge, with the surface of an adhesive layer in such a waythat the surface of material featuring at least one ridge generates, inthe surface of the adhesive layer, a topography of grooves which isessentially the inverse of the topography of the surface of materialfeaturing at least one ridge;and no groove extends to one of the side edges of the adhesive layer.The above definitions of terms such as “groove”, “surface”, etc., applyin full.

The above surface of material is preferably the surface featuring atleast one ridge on the release liner of the invention. The ridgetopography on the surface of the liner of the invention may be obtained,for example, by shaping (embossing methods), primary forming (castfilm), or by printing.

In accordance with the method of the invention, the topography of theliner may be transmitted to the adhesive layer, for example, by directlycoating the liner with the adhesive or by bringing it into contact withthe adhesive by lamination.

A further subject of the invention is an assembly which comprises arelease liner of the invention and a layer of adhesive in direct contactwith the release liner surface featuring at least one ridge, the layerof adhesive having a topography which is essentially the inverse of thetopography of the release liner surface featuring at least one ridge.

1. An adhesive tape comprising at least one adhesive layer, wherein theadhesive layer has at least one groove and no groove extends to one ofthe side edges of the adhesive layer.
 2. The adhesive tape as claimed inclaim 1, wherein the adhesive layer is a coherent adhesive layer.
 3. Theadhesive tape as claimed in claim 1, wherein the adhesive layer isformed of a pressure-sensitive adhesive.
 4. The adhesive tape as claimedin claim 1, wherein the nongrooved surface area of the adhesive layer is50% to 99% of the total surface area of the adhesive layer.
 5. Theadhesive tape as claimed in claim 1, wherein the groove depth is atleast 10 μm.
 6. The adhesive tape as claimed in claim 1, wherein thegroove depth is not more than 100 μm.
 7. The adhesive tape as claimed inclaim 1, wherein the groove width is 10 to 200 μm.
 8. The adhesive tapeas claimed in claim 1, wherein the at least one groove is a permanentgroove.
 9. A release liner having a surface featuring at least oneridge, wherein no ridge extends to one of the side edges of the releaseliner.
 10. The release liner as claimed in claim 9, wherein the areaoccupied by ridges, as a proportion of the release liner surface areafeaturing at least one ridge, is 1% to 50%.
 11. The release liner asclaimed in claim 9, wherein the ridge height is 10 to 100 μm.
 12. Therelease liner as claimed in claim 9, wherein the ridge width at the footof the ridge is 10 to 200 μm.
 13. An assembly comprising a release lineras claimed in claim 9 and a layer of adhesive in direct contact with therelease liner surface featuring at least one ridge, the layer ofadhesive having a topography which is essentially the inverse of thetopography of the release liner surface featuring at least one ridge.14. A method for generating at least one groove in a surface ofadhesive, comprising: contacting a surface of a material, said surfacefeaturing at least one ridge, with a surface of an adhesive layer insuch a way that the surface of material featuring at least one ridgegenerates, in the surface of the adhesive layer, a topography of grooveswhich is essentially the inverse of the topography of the surface ofmaterial featuring at least one ridge; and no groove extends to one ofthe side edges of the adhesive layer.
 15. The method as claimed in claim14, wherein the surface of material is the surface of a release linerthat features at least one ridge.